1. Field of the Invention
The present invention relates to an apparatus for, and method of, lowering items from a drilling rig to a well located below the rig for use in the oil and gas well drilling industry. More particularly, the present invention relates to an apparatus for, and method of, lowering items from a drilling rig through the use of a landing string comprised of drill pipe having an enlarged diameter section with a shoulder, in combination with upper and lower holders having wedge members with shoulders that engage and support the drill pipe at the shoulder of the enlarged diameter section.
2. General Background
Oil and gas well drilling and production operations involve the use of generally cylindrical tubes commonly known in the industry as “casing” which line the generally cylindrical wall of the borehole which has been drilled in the earth. Casing is typically comprised of steel pipe in lengths of approximately 40 feet, each such length being commonly referred to as a “joint” of casing. In use, joints of casing are attached end-to-end to create a continuous conduit. In a completed well, the casing generally extends the entire length of the borehole and protects the production tubing that conducts oil and gas from the producing formation to the top of the borehole, where one or more blowout preventors or production trees may be located on the sea floor.
Casing is generally installed or “run” into the borehole in phases as the borehole is being drilled. The casing in the uppermost portion of the borehole, commonly referred to as “surface casing,” may be several hundred to several thousand feet in length, depending upon numerous factors including the nature of the earthen formation being drilled and the desired final depth of the borehole.
After the surface casing is cemented into position in the borehole, further drilling operations are conducted through the interior of surface casing as the borehole is drilled deeper and deeper. When the borehole reaches a certain depth below the level of the surface casing, depending again on a number of factors such as the nature of the formation and the desired final depth of the borehole, drilling operations are temporarily halted so that the next phase of casing installation, commonly known as intermediate casing, may take place.
Intermediate casing, which may be thousands of feet in total length, is typically made of “joints” of steel pipe, each joint typically being in the range of about 38 to 42 feet in length. The joints of intermediate casing are attached end-to-end, typically through the use of threaded male and female connectors located at the respective ends of each joint of casing.
In the process of installing the intermediate casing, joints of intermediate casing are lowered longitudinally through the floor of the drilling rig. The length of the column of intermediate casing grows as successive joints of casing are added, generally one to four at a time, by drill hands and/or automated handling equipment located on the floor of the drilling rig.
When the last intermediate casing joint has been added, the entire column of intermediate casing, commonly referred to as the intermediate “casing string”, must be lowered further into its proper place in the borehole. The task of lowering the casing string into its final position in the borehole is accomplished by adding joints of drill pipe to the top of the casing string. The additional joints of drill pipe are added, end-to-end, by personnel and/or automated handling equipment located on the drilling rig, thereby creating a column of drill pipe known as the “landing string.” With the addition of each successive joint of drill pipe to the landing string, the casing string is lowered further and further.
During this process as practiced in the prior art, when an additional joint of drill pipe is being added to the landing string, the landing string and casing string hang from the floor of the drilling rig, suspended there by a holder or gripping device commonly referred to in the prior art as “slips.” When in use, the slips generally surround an opening in the rig floor through which the upper end of the uppermost joint of drill pipe protrudes, holding it there a few feet above the surface of the rig floor so that rig personnel and/or automated handling equipment can attach the next joint(s) of drill pipe.
The inner surface of the prior art slips has teeth-like grippers and is curved such that it corresponds with the outer surface of the drill pipe. The outer surface of prior art slips is tapered such that it corresponds with the tapered inner or “bowl” face of the master bushing in which the slips sit.
When in use, the inside surface of the prior art slips is pressed against and “grips” the outer surface of the drill pipe which is surrounded by the slips. The tapered outer surface of the slips, in combination with the corresponding tapered inner face of the master bushing in which the slips sit, cause the slips to tighten around the gripped drill pipe such that the greater the load being carried by that gripped drill pipe, the greater the gripping force of the slips being applied around that gripped drill pipe. Accordingly, the weight of the casing string, and the weight of the landing string being used to “run” or “land” the casing string into the borehole, affects the gripping force being applied by the slips, i.e., the greater the weight the greater the gripping force and crushing effect.
As the world's supply of easy-to-reach oil and gas formations is being depleted, a significant amount of oil and gas exploration has shifted to more challenging and difficult-to-reach locations such as deep-water drilling sites located in thousands of feet of water. In some of the deepest undersea wells drilled to date, wells may be drilled from a rig situated on the ocean surface some 5,000 to 10,000 feet above the sea floor, and such wells may be drilled some 15,000 to 25,000 feet below the sea floor. It is envisioned that as time goes on, oil and gas exploration will involve the drilling of even deeper holes in even deeper water.
For many reasons, including the nature of the geological formations in which unusually deep drilling takes place and is expected to take place in the future, the casing strings required for such wells must be unusually long and must have unusually thick walls, which means that such casing strings are unusually heavy and can be expected in the future to be even heavier. Moreover, the landing string needed to land the casing strings in such extremely deep wells must be unusually long and strong, hence unusually heavy in comparison to landing strings required in more typical wells.
For example, a typical well drilled in an offshore location today may be located in about 300 to 2000 feet of water, and may be drilled 15,000 to 20,000 feet into the sea floor. Typical casing for such a typical well may involve landing a casing string between 15,000 to 20,000 feet in length, weighing 40 to 60 pounds per linear foot, resulting in a typical casing string having a total weight of between 600,000 to 1,200,000 pounds. The landing string required to land such a typical casing string may be 300 to 2000 feet long which, at about 35 pounds per linear foot of landing string, results in a total landing string weight of 10,500 to 70,000 pounds. Hence, prior art slips in typical wells have typically supported combined landing string and casing string weight in the range of between about 610,500 to 1,270,000 pounds.
By way of contrast, extremely deep undersea wells located in 5,000 to 10,000 feet of water, uncommon today but expected to be more common in the future, may involve landing a casing string 15,000 to 20,000 feet in length, weighing 40 to 80 pounds per linear foot, resulting in a total casing string weight of 600,000 to 1,600,000 pounds. The landing string required to land such casing strings in such extremely deep wells may be 5,000 to 10,000 feet long which, at 70 pounds per linear foot, results in a total landing string weight of about 350,000 to 700,000 pounds. Hence, the combined landing string and casing string weight for extremely deep undersea wells may be in the range of 950,000 to 2,300,000 pounds, instead of the 610,500 to 1,270,000 pound range generally applicable to more typical wells. In the future, as deeper wells are drilled in deeper water, the combined landing string and casing string weight can be expected to increase, perhaps up to as much as 4,000,000 pounds or more.
Under certain circumstances, prior art slips have been able to support the combined landing string and casing string weight of 610,500 to 1,270,000 pounds associated with typical wells, depending upon the size, weight and grade of the pipe being held by the slips. In contrast, prior art slips cannot effectively and consistently support the combined landing string and casing string weight of 950,000 to 2,300,000 pounds associated with extremely deep wells, because of numerous problems which occur at such extremely heavy weights.
For example, prior art slips used to support combined landing string and casing string weight above the range of about 610,500 to 1,270,000 pounds have been known to apply such tremendous gripping force that (a) the gripped pipe has been crushed or otherwise deformed and thereby rendered defective, (b) the gripped pipe has been excessively scored and thereby damaged due to the teeth-like grippers on the inside surface of the prior art slips being pressed too deeply into the gripped drill pipe and/or (c) the prior art slips have experienced damage rendering them inoperable.
A related problem involves the uneven distribution of force applied by the prior art slips to the gripped pipe joint. If the tapered outer wall of the slips is not substantially parallel to and aligned with the tapered inner wall of the master bushing, that can create a situation where the gripping force of the slips in concentrated in a relatively small portion of the inside wall of the slips rather than being evenly distributed throughout the entire inside wall of the slips. Such concentration of gripping force in such a relatively small portion of the inner wall of the slips can (a) crush or otherwise deform the gripped drill pipe, (b) result in excessive and harmful strain or elongation of the drill pipe below the point where it is gripped and (c) cause damage to the slips rendering them inoperable.
This uneven distribution of gripping force is not an uncommon problem, as the rough and tumble nature of oil and gas well drilling operations cause the slips and/or master bushing to be knocked about, resulting in misalignment and/or irregularities in the tapered interface between the slips and the master bushing. This problem is exacerbated as the weight supported by the slips is increased, which is the case for extremely deep wells as discussed above.